A major source of food for people in nations around the world is fish. Although highly sophisticated techniques for raising crops (such as grain and vegetables), animals (such as cattle, pigs and sheep), and poultry (such as chickens and turkeys) for human food consumption have evolved over the years, the manner in which fish are obtained for food has changed little over the centuries. Generally, fish grow wild in streams, lakes, and in the oceans, and various techniques for catching these fish for consumption are employed. Commercial fishing operations, while employing more sophisticated boats, nets, and other equipment, still primarily rely upon the hunting, finding, and then netting of fish in the wild to harvest them for eventual human consumption. To obtain fish in this manner is expensive and dependent upon many variables often out of the control of the fishermen themselves. Consequently, obtaining of a reliable regular source of supply of any seafood has not existed.
In addition, the world-wide supply of seafood, particularly gathered from the oceans, is rapidly dwindling due to overfishing by many nations. Consequently, there is a very urgent need to develop techniques for raising fish in a controlled environment, of the types which have been employed for many years in conjunction with the raising of meat animals and poultry. Some types of fish, such as catfish, have been found to be readily adaptable to "fish farm" or controlled growing and harvesting methods to produce a relatively large quantity of fish meat from a relatively small area.
"Fish farms" in the past often simply comprised large ponds supplied with fresh water to make up for that lost through evaporation and into the ground. A problem exists, however, when large numbers of fish are raised in a relatively confined pond since the fish produce significant amounts of solid and liquid wastes. For pond operations, periodic cleaning of the pond bottom to remove the solid wastes produced by the fish must be done to prevent the pond from becoming incapable of use to grow further crops of fish. Often, this required draining the pond. This cleaning is time consuming, expensive, difficult, and messy.
It is necessary, but difficult, to provide a sufficient oxygen content in the water to prevent illness and death of the fish in a pond operation which could result in disastrous financial loss for the "fish farm" operator. Oxygen is provided by the interaction of wind over the water surface; and, if an emergency arises where this is insufficient, air may be temporarily bubbled through the water. Generally, pond culture fish farms require approximately one acre to support 2,000 to 2,500 pounds of fish. Thus, for a large-scale operation, many acres are required.
To reduce the area required for a fish farm operation, the growing of fish, such as catfish and trout in elongated channels or raceways using a combination of recirculating water from the raceway and additional make-up water dropped over a waterfall or the like to aerate the water, have been employed in the past. Waterfall oxygenation systems, however are very inefficient. Thus, systems for bubbling oxygen through the water or for pressurized introduction of oxygen gas to the water have been employed. These systems are expensive. The construction of concrete raceways having a rectangular or circular cross-sectional configuration is generally employed. In the dimensions required for raising fish (approximately six to eight feet wide and four feet deep), it has been necessary to use reinforced concrete. The cost of the raceways is very high and in many cases prohibitive.
Consequently, there is a need for a relatively inexpensive intensive culture system for growing fish in a confined space with efficient oxygenation of the water and which further is self-cleaning to remove wastes produced by the fish.